The invention relates to the positioning of a first element, relative to a second device, through the use of direct current magnetic field generating and receiving devices, and more particularly, to the installation of orthopaedic implants. More particularly, it relates to an improvement over existing devices used for locating holes in an implanted prosthesis so that a screw or pin for interlocking the prosthesis either with itself or with the surrounding bone can be accurately installed. The invention specifically relates to a positioner or aiming (targeting) device for locking screw or pins for such orthopedic hardware which employs pulsed direct current (DC) transmitted signals to enable precise positioning of such screws or pins.
Various intramedullary nails and targeting devices for interlocking the intramedullary nail to the surrounding bone, particularly for the use in repairing the femur, are known in the prior art. One targeting method that is capable of providing precise locating of the holes distally uses x-ray techniques, but long periods of x-ray exposure are required and the need to move the x-ray equipment in and out of position to check the screw or pin locations means that there is a risk of a loss of alignment each time the equipment is moved. Patents of interest in this field include U.S. Pat. No. 5,537,453 (Williams et.al.); U.S. Pat. No. 5,478,343 (Ritter); U.S. Pat. No. 5,426,687 (Goodall et al); U.S. Pat. No. 5,178,621 (Cook, et. al.); U.S. Pat. No. 5,031,203 (Trecha); U.S. Pat. No. 5,030,222 (Calandruccio et al); U.S. Pat. No. 5,013,317 (Cole et al); and others as cited in the above patents. As a consequence of these radiographic techniques, the positioning of such locking screws or pins is typically the most time consuming and difficult portion of the overall rod implantation procedure.
Two other patents are thought to be of more general interest, U.S. Pat. No. 4,625,718 (Olerud et al.), and U.S. Pat. No. 4,570,624 (Wu). The Olerud et al. patent disclosing an aiming apparatus using X-ray techniques for making holes or bores in the bone of a patient in registration with the holes or bores on an interlocking nail, and the Wu patent disclosing a mechanical technique for aligning surgical pins in parallel.
Patents of interest in this field include U.S. Pat. No. 4,621,628 (Brudermann); U.S. Pat. No. 5,049,151 (Durham et al); and U.S. Pat. No. 5,514,145 (Durham et al). The Brudermann patent discloses an apparatus for locating transverse holes in the distal end of implanted locking nails. The apparatus includes at least one magnet which generates an axially symmetrical field, in combination with a magnetic field detecting device or sensor having an axial field reception characteristic. In one embodiment, the magnetic field sensor is inserted into an implanted nail and the magnet, which is placed on the surface of the skin, is moved until axes of the magnetic field of the magnet and the sensor are aligned. More particularly, the sensor is connected to an external display device and alignment of the respective magnetic fields is indicated when a zero-point indication is provided on the display device. A second magnet can be used to increase the precision of the alignment process. The directional characteristics of the magnetic field detection device are used to control the relative positions of the axes of both directional elements through a display device, such that both axes are brought into congruence with each other by means of the control display. When one of the directional elements is aligned exactly with the axis of the of the transverse hole in the in the nail, another element can be used externally to mark the location of the nail hole for positioning of a drilling jig.
The two patents by Durham et al. relate to a method and apparatus for positioning the screws or pins of orthopedic hardware devices such as intramedullary rods which involves the positioning of a first magnet at the location of a screw hole in the nail and then using an aiming device, comprising a second magnet which interacts with the first magnet, to locate the first magnet and hence enable a screw or pin to be placed in the screw hole in the nail to lock the nail in position.
In one first embodiment, an insertion rod is used to position the first magnet at the level of the hole in the rod while in another embodiment, a solid nail is used and the magnet is removable disposed within the hole in the nail prior to implantation of the nail.
One serious disadvantage common to the magnetic field detection devices is the detrimental influence of stray magnetic fields, such as, for example the earth magnetic field, or the effect of field distortion due to highly conductive materials in the form of aluminum, titanium, stainless steel and copper used in the construction of operating room tables and surgical implants. The art of using transmitting and receiving components with electromagnetic coupling for measuring position and orientation is well known especially with respect to armament sighting systems where the receiver component would be located in gunner""s helmet and a transmitter component would be attached to a nearby electrically non-conductive structure. As the gunner would sight-in a target through a sighting cross-hair affixed to his helmet, the receiver located thereupon would pick up signals generated by the transmitter. These signals would then be processed by a computer to determine the position and orientation of the helmet and then to contemporaneously point a unit of armament in the same direction as the helmet mounted sight piece. As taught in U.S. Pat. No. 4,054,881 (Raab) and U.S. Pat. No. 4,287,809 (Egli et al.), and U.S. Pat. No. 4,314,251 (Raab) and U.S. Pat. No. 4,396,885 (Constant), an alternating current (AC) signal is applied in a time division or frequency division format to a transmitter consisting of two or three orthogonal coils which generate an AC electromagnetic field which is measured by an AC receiver likewise consisting of three or two orthogonal coils. These sensed signals are then filtered and amplified in a method compatible with the transmitted format, converted to a digital format and then read into a computer where various mathematical methods are resorted to in order to extract position and orientation with resort to applicable electromagnetic field equations.
All current systems such as the ones above, that utilize an AC transmitted signal work accurately only when there are no electrically conductive materials located near either the transmitter or receiver because any transmitted AC signal would invariably induce eddy currents in these conductive materials which would in turn serve to generate an AC magnetic field that would distort any transmitted field, and, of course, any ultimate out-put position and orientation data. In fighter aircraft or helicopters where it is desired to use these position and orientation measuring systems, there are a lot of highly conductive materials in the form of aluminum, titanium, magnesium, stainless steel, and copper used in the construction of the cockpit structure, seat, wiring and helmet-mounted displays. U.S. Pat. No. 4,287,809 teaches a method of compensating for the errors resulting from any field distortion due to cockpit metal that does not move with respect to the transmitter. The compensation method therein suggested involves making measurements throughout the cockpit to determine the amount of such distortion and then using this data to form a correction that is applied to the sensed signals. In a similar manner, U.S. Pat. No. 4,394,831 (Egli et al.) and U.S. Pat. No. 4,621,628 (Brudermann) teaches a method to accomplish compensation for errors due to eddy currents induced in metal such as would be found in a display located on a pilot""s helmet or operating field, respectively. This compensation method again requires initial experimental measurements of such distortion in order to effect necessary corrections and provides moderate improvements in accuracy only when the amount of metal is concentrated in a single location and the transmitter does not go through large angular rotations or translations. These types of compensation efforts that are required to make AC systems work accurately are time consuming and expensive to perform and only work in environments where there would not be too much conductive material near transmitter or receiver units. In many locations, for example, AC systems cannot be utilized at all because the distortions produced are simply too large to be corrected merely by such mapping.
It is the object of this invention to provide an effective and economical device for the determination of the location and orientation of the holes in orthopaedic implants. Still another object of the present invention is to provide a targeting device which can be utilized by the majority of current intramedullary nails currently available to the surgeon.
The invention includes a two- or three-axis transmitter positioner driven by a pulsed DC current, external to the patient, coupled with three- or two-axis receivers positioned internal and/or external to the implant. The receivers are sensitive to a transmitted DC magnetic field emanating from the activated transmitter. Receiver signal processing electronics control the receiver and serve to convert its output to a format suitable for processing by a digital computer in conjunction with a method for processing received signals so as to thereby develop position and orientation data of the transverse locking holes or pin placement. Such data then can be graphically displayed to the user so as to guide the user for accurate alignment of a drill bit with the transverse holes in the implanted device.
The devices presented in U.S. Pat. Nos. 4,945,305 and 4,849,692 (Blood) represents a radical departure from all of the prior art relating to such transmitting and receiving position and orientation devices, insomuch as it avoids, in-toto, resort to AC signals and instead relies upon direct current (DC) signals. Such reliance on DC signals obviates completely any need for a prior calibration undertakings and greatly expands the potential utility of devices of this type. Moreover, manufacture and utilization of this device for purposes of accomplishing all that current devices can accomplish is manifestly less expensive than such manufacture and utilization of said currently used devices are or potentially will be.
It has now been found that the use of the devices of U.S. Pat. Nos. 4,945,305 and 4,849,692, the disclosure of which are incorporated by reference herein, as though recited infull, can be applied to the installation of orthopaedic implants and, more particularly, to the locating of holes in an implanted prosthesis so that a screw or pin for interlocking the prosthesis either with itself or with the surrounding bone can be accurately installed, with surprising effective results.
The invention provides a system of transmitting and receiving antennae that by themselves intrinsically and with inherent electronic means together with a digital computer readily measure position and orientation relative to one another without the need for expensive calibration procedures undertaken in advance of implementation and further without concern for what types of diamagnetic or paramagnetic metallic materials such as may be nearby. For the first time, for instance, devices of this nature can be used in surgical procedures in conjunction with metallic implants and surgical apparatus.
The invention provides for the determination of the displacement vector and determination of the orientation of the orthogonal axis of the receiver relative to the transmitter, FIG. 1. The transmitter is considered the origin of an orthogonal coordinate system of x, y, and z coordinates wherein the z-axis is considered, generally, in line with the gravitational axis of the earth, the x and y axes then lie in the horizontal plane, perpendicular to the z axis and according to a Cartesian coordinate system. The Cartesian system consists of three mutually perpendicular lines or axes that intersect at a common point such that the location of a point relative to the origin can be determined without ambiguity. In addition, each receiver establishes a reference coordinate system with respect to the respective receiver and relative to the transmitter origin such that the location of the receiver can be determined from the transmitter, as well as the rotation of each axis of the receiver system relative to the transmitter. It is an advantage of the invention that the coordinate reference system of the receiver can be electronically offset to a desired location using the inherent electronic means together with a digital computer. As shown in FIG. 6, the reference axis S1 of receiver 107 at location r1 can be electronically offset to a location r1xe2x80x2 with a reference axis S1xe2x80x2 such that the location vector and the angular orientation of the axis S1xe2x80x2 from the transmitter can be ascertained. Likewise, the receiver axis of each receiver can be offset to any desired positioned.
It is a further advantage of the invention that the relative position and orientation between two or more offset locations can be ascertained using the inherent electronic means together with a digital computer. It is a further advantage that the relative distance between two or more offset axes can be minimized such that one or more of the relative components of the relative displacement vector be minimized and the corresponding axes aligned in space.
The invention provides a distinctly less expensive sighting device than is currently provided within the framework of the present state of the art separate and apart from the cost savings to be realized from abrogation of calibration requirements. Presently, the cores of the transmitting components of these devices are made up of Ferrite. Ferrite is rather expensive, but, in addition to this, it is also rather fragile and difficult to shape. However, Ferrite is necessary as a core piece in order to keep eddy current distortion acceptably low where AC current is used. But, there are no AC signal components in the instant device""s steady state signal and hence, the same magnetic flux concentration as can be had with Ferrite can likewise be had and used with this device by resorting to less expensive iron or steel for a transmitting core piece, since, with this device, there is no need to be concerned with eddy currents at all.
The instant invention provides a targeting apparatus which does not require the use of radiographic radiation in determining the location of the transverse holes of intramedullary implants, particularly of the distal holes of interlocking nail. The apparatus of the present invention provides, fast, convenient and secure placement of the drilling jig in axial alignment with the transverse holes without involving the radiation exposure on the surgeon, patient, and other medical personnel. The current surgical practice in the use of the image intensifier to locate the unseen transverse holes in the implant and to target the hole for drilling and placement of interlocking screws exposes the surgeon to excessive amounts of radiation during the course of the procedure.
Another advantage of the present invention is that it provides a targeting device which can be utilized by the majority of current intramedullary nails currently available to the surgeon. The current mechanical locating devices are usually implant specific and require the use of the image intensifier to locate the orientation of the distal locking holes. The Distal Targeting Device described in the Russell-Taylor Surgical Technique brochure (Smith and Nephew Richards, Memphis Tenn.) is a xe2x80x9cbombsitexe2x80x9d apparatus which is mechanically fastened to the proximal end of the nail and utilizes the image intensifier to locate and drill the necessary holes. The mechanical targeting system described in U.S. Pat. No. 4,913,137 is specific to that device. The targeting mechanism described by Azer et al requires that the described nail have a bifurcated tip, a cross section complimentary to other instrumentation, and a mechanism for attachment to the proximal end of the nail. The rod mounted targeting mechanism described in the surgical technique for the Alta Trauma System by Howmedica (Rutherford, N.J.) requires the initial location of the distal holes, the attachment of the targeting assembly mechanism to the nail, and further fluoroscopic control to position the targeting assembly over the distal holes. Another technique used for the above systems, as well as all the other nail systems, requires the use of direct fluoroscopic imaging to locate and align the holes with out any mechanical or electrical connections is called xe2x80x9cfree handingxe2x80x9d. This technique is described in detail in the brochures by Smith and Nephew Richards, Zimmer (Warsaw, Ind.), Ace Medical (Los Angeles, Calif.) and Biomet (Warsaw, Ind.).
The described technique and devices of the present invention can be customized for any of the described intramedullary nails.
In accordance with the invention, a DC coupled electromagnetic sensor is provided which is easier to use than prior art devices and which provides easier and more accurate alignment than is afforded by the prior art. In this regard, although the positioner arrangement of the Brudermann and Durham et al. patents discussed above possesses a number of important advantages over the radiographic locator devices, the present invention provides important additional advantages over the positioner arrangement disclosed in those patents, particularly in the areas of ease of use and ease and quality of the alignment.
In one aspect of the invention, a DC coupled electromagnetic positioning system is provided for assisting in positioning a fastening element at a desired concealed internal location such as at a locking screw hole in an intramedullary rod in the bone of a patient, the arrangement comprising: a pulsed DC current transmitter, a first receiver, or a plurality of receivers, that is sensitive to the transmitted DC magnetic field adapted to be positioned at said internal location and providing a two or three axis directional reference or coupled with the implant at a known offset location and orientation from the internal location to be positioned; and a second or additional receivers thus providing multiple reference positioning devices external to the patient; the positioning device comprising a hand-held drilling jig or guide drill having an axial bore there through, so as to enable the external receiver to align with the internal or couple receiver, the positioning device further comprising a guide pin insertable into the axial bore and adapted to be engaged by the drill chuck of said drill when the perceived axes of the first and second receivers are aligned so as to enable the guide pin to be advanced by the drill along a path of travel in alignment with the internal location.
In an advantageous embodiment, the said first receiver or internal sensor unit is embedded in a unit or handle to which the implanted device is attached. The location and orientation of the receiver relative to each internal concealed location to be positioned can be known through either physical measurement or electronic determination using a calibration routine. In an advantageous embodiment, the said first receiver or internal unit includes a protective cover. Preferably, the protective cover comprises a plastic casing advantageously shaped to match or conform to the internal shape of the particular intramedullary device being implanted. Thus the embodiment of the invention involves the provision of a locating arrangement that can be used with any commercial nail.
In an advantageous embodiment, the perceived position of the first and second receiver, or additional receivers, relative to the transmitter, can be electronically offset by the connected computer so as to provide a perceived location and axis in space, relative to the sensors. The advantage of this embodiment is that the position and axis of the transverse holes can be ascertained without the sensor being physically at the location. With both the first and second sensors offset to the same position, an axis and location of the transverse hole can be located and a drill or pin passed through the hole without interference from the sensor.